The evaluation and development of correlation for heat transfer and fluid flow characteristics in solar air heaters using gapped transverse wire ribs-An experimental study

This study investigates the performance of solar air heaters featuring gapped transverse ribs as roughness elements, with the objective of evaluating their heat transfer and fluid flow characteristics. The research explores several operational and geometric parameters, including the Reynolds number (Re), which varies from 2000 to 16000, relative roughness pitch (P/e) ranging from 8 to 10, the number of gaps (Ng) varying from 1 to 4 (in four steps), and relative roughness length (Lg/e) shifting from 18.3 to 84 (in four increments). These parameters are essential to the performance of the 360 mm × 1300 mm test section of the roughened solar air heater. The results indicate that as the Reynolds number (Re) increases, the friction factor (f) exhibits a decreasing trend; however, the Nusselt number (Nu) follows increasing trends. The introduction of gaps in the wire ribs initially enhances the Nusselt number (Nu), reaching a maximum value before declining with a further increase in Ng. The highest recorded Nusselt number of 108.63 was observed at Re = 16000, with P/e = 10, Ng = 2, and Lg/e = 43.3. Similarly, the maximum value of friction factor of 0.03588 achieved at P/e = 8, Ng = 2, Lg/e = 43.3 and Re = 2000. Furthermore, predictive correlations for Nu and f have been established, displaying average percentage mean deviations of 13.01 % for Nu and 8.82 % for f when juxtaposed with experimental values calculated through the proposed equations. A comprehensive comparison with previously published literature has also been undertaken to validate the findings, emphasizing their applicability and reliability within the domains of solar energy, space heating, and agricultural crop drying.